Apparatus for normal pressure plasma ignition and method for normal pressure plasma ignition using same

ABSTRACT

Provided are an apparatus for normal pressure plasma ignition and a method for normal pressure plasma ignition using the same. The apparatus for normal pressure plasma ignition of the present invention comprises a wave guide tube wherein microwaves are applied, a dielectric tube that penetrates said wave guide tube and introduces a reactant gas, and an ignition apparatus for normal pressure plasma wherein microwaves are applied in said dielectric tube to turn said reactant gas into plasma, wherein said ignition apparatus penetrates said dielectric tube and includes an ignition rod that emits thermal electrons as said microwaves are applied in said dielectric tube. The apparatus for normal pressure plasma ignition according to the present invention enables ignition to be accomplished without power, so that the problems with the prior art that requires high voltage (excessive power, stability issues) may be avoided at the same time. In addition, the normal pressure plasma ignition apparatus according to the present invention enables movement of the ignition rod inside and outside its dielectric tube so that physical damage to the ignition apparatus due to plasma heat may be prevented, and also affords the effect that the scope of metallic materials used in the ignition apparatus is significantly wider than that of the prior art.

BACKGROUND

1. Field

This disclosure relates to an atmospheric plasma ignition apparatus andan atmospheric plasma ignition method using the same, and moreparticularly, to an atmospheric plasma ignition apparatus, which maymake ignition in a non-electric manner, thus solving many problemscaused by high voltage (e.g., excessive electric power andsafety-related problem), preventing the ignition apparatus from beingphysically damaged due to plasma heat, and allowing to use more kinds ofmetal materials for the ignition apparatus than existing cases, and anatmospheric plasma ignition method using the same.

2. Description of the Related Art

If heat is continuously applied to a gaseous material to increase itstemperature, an aggregate of particles, each having nucleus andelectron, are made. This aggregate is called the fourth phase along withsolid, liquid and gas, and the material in this phase is called plasma.

In modern industries, plasma is used in various fields for varioususages, not only for materials demanding high function, high strength orhigh workability but also for high-tech materials for surface treatmentof various materials, ion injection, deposition and removal oforganic/inorganic film, cleaning work, removal of toxic substances andsterilizing or in electronic and environmental industries. Inparticular. in case of plasma in a vacuum state, the plasma is generatedin a sealed space, so it is difficult to control instant processingconditions. In addition, in a closed system, it is hard to performsuccessive processes that should be carried out while an article ismoving. Further, the vacuum state should be maintained, whichessentially needs a vacuum technique. Moreover, such a system requires alot of cost for installation and operation.

The atmospheric plasma technique is proposed to solve such drawbacks.

The atmospheric plasma does not need a vacuum system, and it may bedirectly applied to an existing production line at an atmosphericpressure without any reaction chamber, so it allows successiveprocessing.

In case of this atmospheric plasma, plasma is generated by supplyingelectrons to a level required for initially generating plasma.

FIG. 1 shows an existing torch portion used for the generation ofplasma, mentioned above. Here, the torch portion means a regionconnected to a waveguide and where plasma is generated as externalelectrons are injected, as well known in the art.

Referring to FIG. 1, a dielectric tube 12 is made of quartz, and itsinner wall is coated with boron nitride 4 having a strong heatresistance to endure high-temperature flame. If a torch gas 8 issupplied from a gas source into the dielectric tube 12, an ignitionapparatus 14 supplies initial electrons necessary for discharge, therebycausing discharge in the dielectric tube 12. At this time, due to anelectromagnetic wave (microwave) with a maximum electric field, plasmais generated in the dielectric tube 12 under an atmospheric pressure. Inthis way, it is possible to generate plasma under an atmosphericpressure without any special vacuum device. High temperature plasmaflame (5,000 to 6,000° C.) is emitted through a torch outlet of thedielectric tube 12.

The ignition apparatus 14 plays a role of generating (or, igniting)plasma by using a high voltage in an atmospheric plasma process. FIG. 2shows an example of an existing atmospheric plasma discharging device,particularly, a microwave plasma discharging device.

Referring to FIG. 2, the existing plasma discharging device isconfigured such that an ignition apparatus 16 generating arc is mountedat an injection part of a torch gas 8, as shown in FIG. 1. This ignitionapparatus 16 is configured in a slant direction to cross, as shown inFIG. 2, and an insulating and sealing spacer 161 is mounted thereto.Also, a power supply line 163 is connected to a lower end of theignition apparatus 16, and conductive metal ignition tips 162 generatinga high voltage arc are connected to an upper end thereof. The conductivemetal ignition tip 162 is installed adjacent to a plasma generationregion through an outer wall of the quartz tube 12, so a high voltagearc is generated between two conductive metal ignition tips 162. In thisway, plasma is generated due to microwave in an electric field area ofthe microwave.

However, the existing plasma ignition apparatus causes a significantpower loss since it should generate a high voltage arc. Further, it isdifficult to control environments operated under a high voltage, andvarious safety-related problems such as electric shocks may occur. Inaddition, since the existing plasma ignition apparatus still remains inthe dielectric tube 12 after plasma is generated, it may be easilyphysically damaged due to the plasma. Thus, in order to avoid such aphysical damage, additional treatments are needed for the ignitionapparatus, which increases process costs. Moreover, the dielectric tubeshould be precisely processed such that the metal tip may be insertedinto the dielectric tube made of quartz, so the overall manufacturecosts for the apparatus are increased.

SUMMARY

This disclosure is to solve the above problems, and therefore thisdisclosure is directed to providing a new plasma ignition apparatus,which is different from an existing plasma ignition method using anapplied voltage.

This disclosure is also directed to providing a plasma ignition methodwhich is more economic and safer.

In one aspect, there is provided an atmospheric plasma ignitionapparatus for making a reaction gas into plasma in a dielectric tube,the reaction gas being introduced into the dielectric tube through awaveguide and microwave being applied to the waveguide, wherein theignition apparatus includes an ignition rod configured through thedielectric tube, the ignition rod emitting thermoelectrons when themicrowave is applied thereto in the dielectric tube. The ignitionapparatus includes a moving means for moving the ignition rod into orout of the dielectric tube through the dielectric tube, and the ignitionrod may be made of metal, particularly tungsten. Also, the moving meansmay be a pneumatic actuator or an electric solenoid, and the ignitionrod may be moved in association with the application of microwave, andthe ignition apparatus may be moved out of the dielectric tube after apredetermined time from the application of microwave.

In another aspect, there is also provided an atmospheric plasma ignitionmethod using microwave, wherein the ignition method includes applyingmicrowave to an ignition rod to emit thermoelectrons, the ignition rodbeing capable of emitting thermoelectrons when microwave is appliedthereto.

The atmospheric plasma ignition method may include: applying microwaveto a waveguide; inserting the ignition rod into a dielectric tube towhich a torch gas is introduced, through the waveguide to which themicrowave is applied; generating plasma by the thermoelectrons emittedfrom the ignition rod; and moving the ignition rod out of the dielectrictube after plasma is generated, and the ignition rod may be made ofmetal, particularly tungsten.

Said moving the ignition rod out of the dielectric tube may include:sensing an increase of temperature caused by the generation of plasma;and moving the ignition rod out in case the temperature of the ignitionrod is increased above a preset temperature, or may include: sensing thechange of light caused by the generation of plasma; and moving theignition rod out after the sensing.

The atmospheric plasma ignition apparatus disclosed herein allowsignition in a non-electric manner, so problems caused by a high voltagesuch as excessive power and safety-related problems may be solved. Also,in the atmospheric plasma ignition apparatus disclosed herein, since anignition rod may be moved into or out of a dielectric tube, it ispossible to prevent the ignition apparatus from being physically damageddue to plasma heat. Further, much more kinds of metal materials can beused for the ignition apparatus, in comparison to existing cases.

BRIEF DESCRIPTION OF THE DRAWINGS

The above and other aspects, features and advantages of the disclosedexemplary embodiments will be more apparent from the following detaileddescription taken in conjunction with the accompanying drawings inwhich:

FIG. 1 is a schematic view showing an existing torch portion for plasmageneration;

FIG. 2 shows an example of an existing atmospheric plasma dischargingdevice, particularly a microwave plasma discharging device;

FIG. 3 is a schematic view showing an atmospheric plasma ignitionapparatus disclosed herein;

FIGS. 4 to 6 are schematic views showing the ignition apparatusaccording to one embodiment disclosed herein for illustrating each stageof an ignition operation of an atmospheric plasma; and

FIG. 7 is a flowchart illustrating an atmospheric plasma ignition methodaccording to one embodiment disclosed herein.

DETAILED DESCRIPTION

Exemplary embodiments now will be described more fully hereinafter withreference to the accompanying drawings, in which exemplary embodimentsare shown. This disclosure may, however, be embodied in many differentforms and should not be construed as limited to the exemplaryembodiments set forth therein. Rather, these exemplary embodiments areprovided so that this disclosure will be thorough and complete, and willfully convey the scope of this disclosure to those skilled in the art.In the description, details of well-known features and techniques may beomitted to avoid unnecessarily obscuring the presented embodiments.

The terminology used herein is for the purpose of describing particularembodiments only and is not intended to be limiting of this disclosure.As used herein, the singular forms “a”, “an” and “the” are intended toinclude the plural forms as well, unless the context clearly indicatesotherwise. Furthermore, the use of the terms a, an, etc. does not denotea limitation of quantity, but rather denotes the presence of at leastone of the referenced item. The use of the terms “first”, “second”, andthe like does not imply any particular order, but they are included toidentify individual elements. Moreover, the use of the teens first,second, etc. does not denote any order or importance, but rather theterms first, second, etc. are used to distinguish one element fromanother. It will be further understood that the terms “comprises” and/or“comprising”, or “includes” and/or “including” when used in thisspecification, specify the presence of stated features, regions,integers, steps, operations, elements, and/or components, but do notpreclude the presence or addition of one or more other features,regions, integers, steps, operations, elements, components, and/orgroups thereof.

Unless otherwise defined, all terms (including technical and scientificterms) used herein have the same meaning as commonly understood by oneof ordinary skill in the art. It will be further understood that terms,such as those defined in commonly used dictionaries, should beinterpreted as having a meaning that is consistent with their meaning inthe context of the relevant art and the present disclosure, and will notbe interpreted in an idealized or overly formal sense unless expresslyso defined herein.

In the drawings, like reference numerals in the drawings denote likeelements. The shape, size and regions, and the like, of the drawing maybe exaggerated for clarity.

An ignition apparatus disclosed herein utilizes thermoelectron emissionof metal, instead of an existing arc method requiring application of ahigh voltage. In an existing method an atmosphere plasma is generated byapplying a high voltage to a metal electrode such as tungsten in aregion where plasma is not generated. However, in this case, there aremany problems such as economic loss caused by high voltage,safety-related problems, expensive equipments required for applying ahigh voltage, and so on. In addition, since the metal electrode such astungsten is directly exposed to a plasma heat, it may be physicallydamaged.

The inventors found that, in case an ignition rod allowing thermoionicemission like tungsten is inserted into a dielectric tube to which amicrowave is applied, thermoelectrons are emitted from the ignition rod,and, if thermoelectrons are emitted to a level required for initiallyigniting plasma, the generation of plasma is initiated. Further, theinventors completed this invention with the conception that the ignitionapparatus may freely move through the dielectric tube since thepressures in and out of the dielectric tube where plasma is generatedare identical to each other.

Hereinafter, the disclosure is described in more detail with referenceto the accompanying drawings.

FIG. 3 is a schematic view showing an atmospheric plasma ignitionapparatus disclosed herein.

Referring to FIG. 3, the atmospheric plasma ignition apparatus disclosedherein includes an ignition rod 310 for emitting electrons when heat isgenerated due to microwaves, and a moving means 300 connected to theignition rod 310 to automatically move the ignition rod 310. Theignition rod may be made of any material capable of emittingthermoelectrons by means of microwaves, preferably tungsten that easilyemits thermoelectrons. However, any kind of metal capable of emittingthermoelectrons may be used, not limited to tungsten.

The moving means may adopt any means capable of moving the ignition rodwhen an external signal or pressure is applied thereto. In other words,various kinds of moving means used in the related art such as apneumatic actuator or an electric solenoid may be used, and any kind ofmoving means capable of moving the ignition rod may be selected as theabove moving means.

The ignition apparatus disclosed herein does not need a special moldingof a dielectric tube for insertion of a metal tip into the dielectrictube, differently from an existing case as shown in FIG. 2. Thus, theoverall manufacture cost for an atmospheric plasma manufacturing systemmay be decreased.

Hereinafter, the operation principle of the atmospheric plasma ignitionapparatus is explained with reference to the accompanying drawings.

FIGS. 4 to 6 are schematic views showing the ignition apparatusaccording to one embodiment disclosed herein for illustrating each stageof an atmospheric plasma ignition operation.

Referring to FIG. 4, the atmospheric plasma system according to oneembodiment disclosed herein includes a magnetron (not shown) forgenerating microwave, a waveguide through which the microwave istransmitted from the magnetron, and a dielectric tube provided with anignition apparatus disclosed herein and to which a torch gas isintroduced through the waveguide. The torch gas may be inert gas such ashelium and argon, but is not limited thereto.

The ignition rod 410 may be located in or out of the dielectric tube,and FIG. 4 shows the plasma ignition apparatus having the ignition rod410 out of the dielectric tube.

FIG. 5 is a schematic view showing that microwave is applied to thewaveguide and the dielectric tube as the plasma process is initialed,and also the ignition rod 410 of the ignition apparatus is inserted intothe dielectric tube.

Referring to FIG. 5, the temperature of the ignition rod 410 increasesrapidly due to the applied microwave and, as a result, thermoelectronsare emitted from the ignition rod. If an amount of emittedthermoelectrons is continuously increased, the reaction gas is turnedinto plasma.

The shape and material of the ignition rod are not specially limited asmentioned above, but the ignition rod may have a structure capable ofeffectively guiding emission of thermoelectrons. For example, theignition rod may be configured such that its end converges to one point.In this case, thermoelectrons may be sufficiently emitted from thepointed end.

FIG. 6 is a schematic view after plasma ignition.

Referring to FIG. 6, after plasma is ignited, the ignition rod of theignition apparatus is moved out of the dielectric tube. If the ignitionrod remains in the dielectric tube, it is difficult to control plasmadue to the emission of excessive thermoelectrons, and also the ignitionrod may be damaged due to plasma heat. Further, a volume loss of plasmacaused by the existence of the ignition rod is also expected.

Such problems are solved by moving the ignition rod usingcharacteristics of the atmospheric plasma (Since the pressures in andout of the dielectric tube are identical to each other, the ignition rodmay be moved).

In another embodiment, the ignition rod may be automatically moved.

In other words, in case a user sets a period during which sufficientthermoelectrons are emitted after microwave is applied, after themicrowave turns on, the ignition rod may keep an inserted state in thedielectric tube during the preset period. Then, after a predeterminedtime (namely, after the plasma is ignited), the ignition rod is movedout of the dielectric tube.

The automatic movement of the ignition rod may be performed by sensingthe temperature of the ignition rod or the dielectric tube. When plasmais initially generated, temperature is inevitably increased. In thiscase, the temperature of the dielectric tube or the ignition rod is alsoincreased. Thus, while monitoring the increase of temperature, it ispossible to move the ignition rod out of the dielectric tube in case thetemperature is increased.

As an alternative, it is also possible to sense the change of light, forexample UV, caused by generation of plasma. When plasma is initiallygenerated, light is emitted to an observable level at the outside. Inthis case, a photo sensor, for example a UV sensor, may be used todetermine whether plasma is generated, and if UV is generated to a levelcapable of recognizing the generation of plasma, the ignition rod ma bemoved out of the dielectric tube.

The ignition apparatus described above is operated to ignite plasma byapplying microwave to the ignition rod which is capable of emitting freeelectrons.

Hereinafter, an ignition method using the ignition apparatus explainedabove is described in detail with reference to the accompanyingdrawings.

FIG. 7 is a flowchart showing an atmospheric plasma ignition methodaccording to one embodiment disclosed herein.

Referring to FIG. 7, first, microwave is applied through the waveguide.After that, the ignition rod moves through the waveguide to which themicrowave is applied, and then the ignition rod is inserted into thedielectric tube into which a torch gas is introduced. At this time, themicrowave heats the ignition rod, and as a result thermoelectrons areemitted from the ignition rod.

After the thermoelectrons are emitted more than required for generatingplasma, the plasma is generated in the dielectric tube. This generationof plasma is explained in more detail below through an experimentalexample.

Since the atmospheric plasma ignition method disclosed herein allowsignition of plasma due to the emission of electrons by microwaveswithout applying a high voltage, this method is very energy-efficient.Also, since plasma is generated under atmospheric conditions, theignition rod may be moved out of the dielectric tube right after theinitial ignition, so the life span of the ignition apparatus may beextended.

Detailed aspect and configuration of the atmospheric plasma ignitionmethod disclosed herein are based on the above atmospheric plasmaignition apparatus, and will not be explained in detail again.

EXAMPLES

The examples and experiments will now be described. The followingexamples and experiments are for illustrative purposes only and notintended to limit the scope of this disclosure.

Plasma Generation Experiment

While applying microwave of 2.45 GHz, 10 to 30 lpm of torch gas (helium)was flown to an atmospheric plasma system as shown in FIG. 3 for 5 to 10seconds. After that, an ignition rod (tungsten) of the ignitionapparatus was inserted into a reactor (into the dielectric tube).

Right after the ignition rod was inserted into the waveguide, theignition rod was heated by means of microwave applied into thewaveguide, and then thermoelectrons were emitted to generate arc. Also,after 1 to 5 seconds from the insertion of the ignition rod, plasma wasgenerated.

Through this experimental example and pictures, it could be understoodthat atmospheric plasma may be effectively generated in the waveguide bymeans of a mechanical method, i.e. the insertion of the ignition rod.

While the exemplary embodiments have been shown and described, it willbe understood by those skilled in the art that various changes in formand details may be made thereto without departing from the spirit andscope of this disclosure as defined by the appended claims.

In addition, many modifications can be made to adapt a particularsituation or material to the teachings of this disclosure withoutdeparting from the essential scope thereof. Therefore, it is intendedthat this disclosure not be limited to the particular exemplaryembodiments disclosed as the best mode contemplated for carrying outthis disclosure, but that this disclosure will include all embodimentsfalling within the scope of the appended claims.

1. An atmospheric plasma ignition apparatus for making a reaction gas into plasma in a dielectric tube, the reaction gas being introduced into the dielectric tube through a waveguide and microwave being applied to the waveguide, wherein the ignition apparatus comprises an ignition rod configured through the dielectric tube, the ignition rod emitting thermoelectrons when the microwave is applied thereto in the dielectric tube.
 2. The atmospheric plasma ignition apparatus according to claim 1, wherein the ignition apparatus comprises a moving means for moving the ignition rod into or out of the dielectric tube through the dielectric tube.
 3. The atmospheric plasma ignition apparatus according to claim 1, wherein the ignition rod is made of metal.
 4. The atmospheric plasma ignition apparatus according to claim 3, wherein the metal comprises tungsten.
 5. The atmospheric plasma ignition apparatus according to claim 2, wherein the moving means is a pneumatic actuator or an electric solenoid.
 6. The atmospheric plasma ignition apparatus according to claim 2, wherein the ignition rod is moved in association with the application of microwave, and the ignition apparatus is moved out of the dielectric tube after a predetermined time from the application of microwave.
 7. An atmospheric plasma ignition method using microwave, comprising applying microwave to an ignition rod to emit thermoelectrons, the ignition rod being capable of emitting thermoelectrons when microwave is applied thereto.
 8. The atmospheric plasma ignition method according to claim 7, comprising: applying microwave to a waveguide; inserting the ignition rod into a dielectric tube to which a torch gas is introduced, through the waveguide to which the microwave is applied; generating plasma by the thermoelectrons emitted from the ignition rod; and moving the ignition rod out of the dielectric tube after plasma is generated.
 9. The atmospheric plasma ignition method according to claim 7, wherein the ignition rod is made of metal.
 10. The atmospheric plasma ignition method according to claim 9, wherein the metal comprises tungsten.
 11. The atmospheric plasma ignition method according to claim 8, wherein said moving the ignition rod out of the dielectric tube comprises: sensing an increase of temperature caused by the generation of plasma; and moving the ignition rod out in case the temperature of the ignition rod is increased above a preset temperature.
 12. The atmospheric plasma ignition method according to claim 8, wherein said moving the ignition rod out of the dielectric tube comprises: sensing a change of light caused by the generation of plasma; and moving the ignition rod out after said sensing. 